The Mechanical Properties and Microstructure of Reticulated Red Clay-Sand Mixture Using X-Ray Diffraction

To assess the behavior of Reticulated Red Clay (RRC)-sand mixtures, a series of laboratory tests were performed on RRC-sand mixtures in which the weight ratio of sand ranging from 0% to 80%. Compaction test and direct shear test were conducted to evaluate the compactness of mixtures. The threshold sand content for the change of the mechanical properties of the mixture is 50%, and the mixture at this time has the densest structure. Oedometer test to the mixture indicate that the coefficient and compression modulus of it are only related to the ratio of its components. As the sand content in the mixture increases, the phenomena that the clay particles enclosing the sand particles and filling into the gaps of particles make the mixture denser. During the same time, there is a phenomenon of internal friction between sand particles caused by the inadequate wrapping of clay particles. Combined with the results of scanning electron microscopy and optical microscopy, the appearance of these phenomena and the transition process of the structure of the mixture from the clay structure to the sand structure were confirmed.

Growth responses of C3 and C4 crops to soil physico-chemical properties in Rivers State, Nigeria

This study evaluated the growth responses of C3 and C4 crops to soil physico-chemical properties in Rivers State. The C3 crop refers to Pumpkin and Cucumber while C4 crop refers to Amaranthus in this study. The research work made use of three crops (Pumpkin, Cucumber and Amaranthus in some selected sites in Rivers State and the study was carried out both in the dry and wet seasons. Soil samples were collected from both topsoil (0-15cm) and subsoil (15-30cm). The crops and soil samples were taken to the laboratory for further analysis. Mean values and standard deviations were used to describe the analysis while analysis of variance (ANOVA), Duncan, and Kruskal Wallis were used to test the hypotheses. All analyses were carried out using Statistical Package for Social Sciences (SPSS) 21.1 Version. Findings showed that sand content in Oyigbo had the highest in the topsoil at 95.37% while Etche had highest in silt content at 1.87%. For the subsoil, Oyigbo also had the highest sand content at 93.30% while Ikwerre had the highest clay content at 6.63% in subsoil. For chemical properties of soil, total organic carbon and magnesium were highest in Oyigbo at 1.91% and 24.00% respectively for topsoil while for subsoil potassium was highest in Ikwerre at 8.30%. It was also discovered C3 and C4 crops planted in Oyigbo, Etche and Ikwerre varied from the nutrients standards recommended by USDA (2014). The following nutrients and minerals were considered: energy, carbohydrates, protein, total fat, cholesterol, dietary fiber, vitamins, folates, niacin, pantogenic acid, pyridoxine, riboflavin, thiamin, Electrolytes, sodium, potassium, calcium, iron, magnesium, manganese phosphorus, and zinc. For standards recommended by (USDA 2014), only energy, iron, zinc, manganese, vitamin E, riboflavin, pyridoxine, niacin and pantothenic acid at Oyigbo met the standards, also Riboflavin and iron at Ikwerre met the (USDA 2014) standards while only folates at Etche met the (USDA 2014) standards. The study recommended that the soil nutrients and pH should be improved across the three locations and the acidic nature of both topsoil and subsoil should be improved by neutralizing the soil with lime.

On Random Subspace Optimization-Based Hybrid Computing Models Predicting the California Bearing Ratio of Soils

The California Bearing Ratio (CBR) is an important index for evaluating the bearing capacity of pavement subgrade materials. In this research, random subspace optimization-based hybrid computing models were trained and developed for the prediction of the CBR of soil. Three models were developed, namely reduced error pruning trees (REPTs), random subsurface-based REPT (RSS-REPT), and RSS-based extra tree (RSS-ET). An experimental database was compiled from a total of 214 soil samples, which were classified according to AASHTO M 145, and included 26 samples of A-2-6 (clayey gravel and sand soil), 3 samples of A-4 (silty soil), 89 samples of A-6 (clayey soil), and 96 samples of A-7-6 (clayey soil). All CBR tests were performed in soaked conditions. The input parameters of the models included the particle size distribution, gravel content (G), coarse sand content (CS), fine sand content (FS), silt clay content (SC), organic content (O), liquid limit (LL), plastic limit (PL), plasticity index (PI), optimum moisture content (OMC), and maximum dry density (MDD). The accuracy of the developed models was assessed using numerous performance indexes, such as the coefficient of determination, relative error, MAE, and RMSE. The results show that the highest prediction accuracy was obtained using the RSS-based extra tree optimization technique.

Study on the Effect and Mechanism of Alkali–Silica Reaction Expansion in Glass Concrete

The suppression of ASR expansion hazards of glass concrete has always been a key and hot issue in the research of glass concrete. According to the ASTM C1260-14 fast mortar rod method, glass sand and glass powder act as fine aggregate and auxiliary cementing material, respectively. The changes in expansion rate with different amounts of glass sand content and different particle sizes of glass powder in mortar rods were compared, and the effects of glass sand content and the glass powder particle size on the expansion of ASR were analyzed. SEM was used to compare and analyze the microstructure of mortar rods to explore the mechanism of ASR expansion of glass concrete, and the results showed that the addition of glass powder had a certain inhibitory effect on ASR expansion. The larger the particle size of glass powder was, the better the inhibition effect on ASR expansion and the longer its duration. Compared with the three groups of experiments of 0–13 μm, 13–38 μm, and 38–75 μm, it was found that the influence of the glass powder particle size on the expansion of ASR was weaker than that of dosage. The inhibitory effect of glass powder on ASR expansion is related to the fact that glass powder is more involved in pozzolanic reaction in the early hydration process.

The Influences of Sand Content and Particle Size on the Desiccation Cracks of Compacted Expansive Soil

The desiccation cracks in expansive soil, which are a common natural phenomenon, have a significant negative impact on the engineering properties of the soil and are the direct cause of many engineering problems and geological disasters. This study aims to investigate the influences of sand content and particle size on desiccation cracks of the compacted expansive soil. First, samples of compacted expansive soil with five sand contents and four sand size groups were prepared. Then, a series of drying tests were performed. The dynamic variation of geometric parameters of the surface crack network during evaporation was quantitatively analyzed by using digital image processing technology and fractal theory. The results demonstrated that the increase of the surface-cracking areas in the early and later stages was manifested by the increase of the crack length and crack width, respectively. In the same size of sand particle group (0.15, 0.3 mm), as the sand content (dry weight ratio of soil sample) increased from 0% to 40%, the surface-cracking ratio (the ratio of the crack area to the total surface area of the soil sample) showed a decreasing trend (13.20%, 11.42%, 10.50%, 8.98%, and 7.71%, respectively). When the sand content (40%) was the same, as the sand size groups increased from [0.15 mm, 0.3 mm) to [1.18 mm, 2.36 mm), the surface-cracking ratio also presented a decreasing trend (7.71%, 7.69%, 4.35%, and 3.73%, respectively). The changing law of the fractal dimension of cracks was the same as that of the surface crack ratio. During the drying process, the deformation of the sample was characterized by centripetal shrinkage or cracking, which were mainly affected by the boundary conditions of the sample. This research’s results verify the effectiveness of sand to improve the dry-shrinkage characteristics of expansive soil, providing a reference for the improvement of roadbeds and the treatment of soil slopes in expansive soil areas.

Exploring Efficiency of Biochar in Enhancing Water Retention in Soils with Varying Grain Size Distributions using ANN Technique

Recently, incentives have been provided in many countries, including Canada and Denmark, to produce biochar for construction usage. This is done because biochar is carbon negative and can help achieve the emission reduction goal of 2030. This technical note aims to analyze the efficiency of biochar in soils with varying grain size distribution for enhancing water retention capacity (WRC). The combinations of biochar content and grain size distributions corresponding to the maximum and minimum efficiency were explored. Artificial Neural Network (ANN) based model for predicting Soil Water Characteristic Curve (SWCC) as a function of soil suction and grain size distribution was developed. A new factor (the ratio of fine (silt + clay) and coarse (sand) content) was proposed for the interpretation of the efficiency of biochar in soils. The newly developed model is able to predict SWCC reasonably well. Biochar amendment is found to influence both dry and wet sides of soils with a clay content lower than threshold content (6–8%). Beyond threshold content, the influence of biochar appears to reduce. However, in the case of high sand content soils (90%), the NWC value on the drier side is generally higher as compared to soils with lower sand content. Based on sensitivity analysis, it was found that the ratio of fine to sand content is the most influential, while biochar content is the least influential.